Semiconductor dies include collections of transistors and other components in an active layer fabricated on substrates. Commonly, these substrates are semiconductor materials, and, in particular, silicon. Additionally, these substrates are conventionally thicker than necessary to obtain desirable device behavior. Conventionally, the layers are deposited on semiconductor wafers that are cingulated or diced to form semiconductor dies.
Thick substrates have advantages during semiconductor manufacturing outside of transistor behavior. During manufacturing of wafers and/or dies, a substrate endures dozens of processes, high temperatures, and transfers between tools or even fabrication sites. During these transfers the substrate can break, resulting in a loss of time and resources. Thick substrates are less likely to break during manufacturing.
Materials deposited on the substrate may have a different stress than the substrate resulting in unbalanced stress. When the stress between the substrate and deposited materials is unbalanced, the substrate may warp or bend to reach an equilibrium stress. Thick substrates are able to counterbalance the stress imposed by deposited materials better than thin substrates. Problems with using thin substrates during manufacturing have conventionally been solved by attaching the thin substrate to a thick support substrate by adhesives. The support substrate is referred to as a carrier wafer. The carrier wafer is detached after completion of the portions of the manufacturing process during which the thin substrate is at risk of fracturing.
Use of a carrier wafer is undesirable for several reasons. The carrier wafer adds cost to manufacturing but does not add tangible value to the final product. Additionally, the adhesives that attach the carrier wafer to the thin substrate leave residue on the thin substrate of the semiconductor wafer. Although the carrier wafer provides stability during manufacturing, releasing the thin substrate from the carrier wafer represents a manufacturing challenge.
One example of manufacturing using a thin substrate is construction of stacked ICs. Stacked ICs increase device functionality and decrease die size by stacking dies vertically. Similar to high-rise towers that fit more office space in a smaller land area, stacked ICs offer more space for transistors and other components while occupying the same area.
In stacked ICs, a second die is stacked on a first die allowing construction to expand into three dimensions (3D). Stacked ICs allow products with a greater number of components to fit in small form factors. Component density of a semiconductor die is number of components in the die divided by the die area. For example, stacking a die on an identical die results in approximately double the number of components in the same area to double component density. When a second die is stacked on a first die, the two dies share the same packaging and communicate to external devices through the packaging.
Conventionally, the second die is coupled to packaging and external devices with through silicon vias located in the first die. Through silicon vias are limited in aspect ratio based, in part, on the manufacturing technique selected. As a result, the height of the first die is limited in order to ensure the through silicon via may extend the entire height of the first die. The through silicon via should extend the entire height to obtain a conducting path from a packaging substrate to the second die. As the height of the first die decreases to accommodate the through silicon via manufacturing, the first die loses structural strength.
Manufacturing a stacked IC conventionally includes attaching a first die to a carrier wafer for support before thinning the first dies. The first dies is then thinned to accommodate the height of the through silicon vias. The wafer of the first dies should be released from the carrier wafer after thinning to package the stacked IC. However, once released from the carrier wafer, the first die may have an unbalanced stress between the substrates of the first dies and any active layers in the dies.
Thus, there is a need for semiconductor manufacturing of thin substrates that reduces risk to the thin substrates without using a carrier wafer.